The overall objective is to determine how the structure and dynamics of low molecular weight cytochromes relate to their function as electron transport catalysts. Cytochromes are ubiquitous electron transport proteins found in all cell lines. An understanding of their function will provide fundamental knowledge into a central process of energy metabolism. The main technique will be NMR spectroscopy with accent on two dimensional solution studies. The primary experimental systems are cytochromes c551 from Pseudomonas aeruginosa and Pseudomonas stutzeri. The specific aims are to (a) assign their proton spectra in the oxidized and reduced forms, (b) compare their structures to each other and to larger eukaryotic cytochromes, (c) determine the kinetics of amide NH exchange as a probe for internal flexibility, and, (d) assess the importance of non-amino acid elements in determining the final tertiary conformation.